Laser oscillator device

ABSTRACT

A laser oscillator device comprises an electric-discharge tube (1) for producing an electric discharge in a laser gas contained in the electric-discharge tube for laser excitation, an optical resonator (2, 3) for effecting laser oscillation, and a gas circulating device having a gas blower (15) and a cooling unit (8) for forcibly cooling the laser gas. The gas blower (15) has an impeller (16) rotatable in the laser gas. An electric motor for driving the turbo impeller has a stator (20) cooled by thermal contact with a water-cooled medium (25) or an air-cooled medium, and a rotor (19) cooled by contact with a gas flowing between the rotor (19) and the stator (20). The motor for driving the turbo impeller can thus sufficiently be cooled.

TECHNICAL FIELD

The present invention relates to a high-power laser such as a machiningCO₂ laser or the like, and more particularly to an improved turbo blowerfor use in a CO₂ laser.

BACKGROUND ART

FIG. 3 of the accompanying drawings shows a conventional CO₂ laseroscillator device. The laser oscillator device includes anelectric-discharge tube 1 having an output coupling mirror 2 and a totalreflection mirror 3 that are positioned in opposite ends of theelectric-discharge tube 1. Metal electrodes 4, 5 are installed on theouter circumference of the electric-discharge tube 1. When ahigh-frequency voltage is applied between the metal electrodes 4, 5 by ahigh-frequency power supply 6, a high-frequency glow discharge isproduced in the electric-discharge tube 1 for laser excitation. A laserbeam axis in the electric-discharge tube 1 is indicated at 13, whereas alaser beam axis extending out of the tube 1 from the output couplingmirror 2 is indicated at 14.

To start the laser oscillator device, a gas in the device is firstevacuated by a vacuum pump 12. Then, a valve 11 is opened to introduce aprescribed amount of laser gas from a gas container 10 into the deviceuntil the pressure of the gas in the device reaches a predeterminedpressure level. Subsequently, the device is continuously evacuated bythe vacuum pump 12 and continuously replenished with the laser gasthrough the valve 11. The laser gas in the device is thereforecontinuously replaced with a fresh gas while the gas pressure in theapparatus is being kept at the predetermined pressure level. In thismanner, the laser gas in the device is prevented from beingcontaminated.

In FIG. 3, the laser gas is circulated in the device by a roots blower 9so that the laser gas is cooled. With the CO₂ gas laser, about 20% ofthe applied electric energy is converted into a laser beam, and the restis consumed to heat the laser gas. According to the theory, however,since the gain of laser oscillation is proportional to the minus (3/2)thpower of the absolute temperature T, it is necessary to forcibly coolthe laser gas in order to increase the oscillation efficiency. In theillustrated device, the laser gas flows through the electric-dischargetube 1 in the direction indicated by the arrows at a speed of about 100m/sec. and is introduced into a cooling unit 8. The cooling unit 8mainly removes the heat energy produced by the electric discharge fromthe laser gas. Since the gas blower 9 heats the laser gas when itcompresses the laser gas, the laser gas from the gas blower 9 is passedthrough a cooling unit 7 before the laser gas is introduced into theelectric-discharge tube 1 again. The cooling units 7, 8 will not bedescribed in detail as they are well known in the art.

The conventional laser oscillator device illustrated in FIG. 3 has thefollowing problems:

The first problem is that since the roots blower is a low-speedvolumetric blower, it is large in size and weight, and the laseroscillator itself is large.

According to the second problem, the roots blower sends a pulsating gasflow, and the output power of the laser is affected by the pulsating gasflow.

The third problem is that the roots blower 9 produces a considerablelevel of vibration which adversely affects the pointing stability of thelaser beam.

DISCLOSURE OF THE INVENTION

In view of the aforesaid problems of the conventional laser oscillatordevice, it is an object of the present invention to provide a laseroscillator device employing a turbo blower.

To achieve the above object, there is provided in accordance with thepresent invention a laser oscillator device comprising anelectric-discharge tube for producing an electric discharge in a lasergas contained in the electric-discharge tube for laser excitation, anoptical resonator for effecting laser oscillation, and a gas circulatingdevice having a gas blower and a cooling unit for forcibly cooling thelaser gas, characterized in that the gas blower comprises a turboimpeller rotatable in the laser gas and an electric motor for drivingthe turbo impeller, the electric motor having a stator cooled by thermalcontact with a water- or air-cooled medium and a rotor cooled by contactwith a gas flowing between the rotor and the stator.

Since the gas blower comprises a turbo blower, its size and weight aresmall, and the gas discharged by the gas blower is not subject topulsations.

The stator of the electric motor for driving the turbo impeller iscooled by thermal contact, and the laser gas for cooling the rotor isguided between the rotor and the stator so that the rotor is cooled bythe flow of the laser gas. Therefore, the electric motor is preventedfrom being excessively heated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a laser oscillator device accordingto an embodiment of the present invention;

FIG. 2 is a cross-sectional view of a turbo blower; and

FIG. 3 is a cross-sectional view of a conventional laser oscillatordevice for a CO₂ laser.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will hereinafter be describedwith reference to the drawings.

FIG. 1 shows a laser oscillator device according to an embodiment of thepresent invention. Those parts in FIG. 1 which are identical to those ofFIG. 3 are denoted by identical reference numerals, and will not bedescribed in detail below. The structure of the electric-discharge tube1, the high-frequency power supply 6 for exciting the gas, and thesupply of a fresh gas from the gas container 10 are identical to thoseof FIG. 3, and will not be described below. Only those elements whichare characteristic of the invention will be described below.

The present invention resides in that a turbo blower 15 is employed inplace of the roots blower 9 shown in FIG. 3. Since the turbo blower 15has a much higher efficiency than the roots blower 9, the heat producedupon compression of the gas is negligible, and hence the cooling unit 7downstream of the blower as shown in FIG. 3 may be dispensed with.Though no cooling unit 7 is shown in FIG. 1, such a cooling unit may beadded.

FIG. 2 shows the structure of the turbo blower. The turbo blowerincludes a turbo impeller 16. The impeller 16 is shown as being acentrifugal impeller, but may be a mixed flow impeller or an axial-flowimpeller. The turbo impeller 16 is mounted on a shaft 17, and rotated ata high speed of about 100,000 RPM by an electric motor comprising arotor 19 and a stator 20, the motor being disposed in a casing 18 whichis separate from a casing in which the laser gas flows. Therefore, thevolume of the turbo blower is smaller than that of a roots blower whichrotates at a lower speed, the volume being in inverse proportion to therotational speed. The shaft 17 is supported by bearings 21, 22 withrolling elements, which are lubricated by grease. With the constructionof the present invention, the heat produced by the motor requires muchconsideration. At the high speed of 100,000 RPM, the motor efficiency isnormally about 75%. Thus, a motor having an output power of 2 KW causesa loss of 500 W which is responsible for the heating of the rotor 19 andthe stator 20. As shown in FIG. 2, the stator 20 is held in closecontact with the wall of the casing 18 which is cooled by water coolingpipes 25 for indirectly cooling the stator 20.

It is more difficult to cool the rotor 19 since it rotates at a highspeed in the laser gas that is leaner than the atmosphere. The heat ofthe rotor 19 is transmitted to the shaft 17 to expand the same. When theshaft 17 is expanded, the clearance around the impeller 16 may vary, thebearings may be broken, the grease may be evaporated, the motorefficiency may be lowered, and the motor may be damaged.

According to the present invention, the rotor 19 is forcibly cooled bypart of the laser gas flowing around the rotor 19. With a CO₂ laserhaving an output power of 1 KW, when the oscillation efficiency is 20%,the laser oscillator device causes a heat loss of 4 KW, which is carriedby the entire laser gas stream that is displaced by the turbo impeller16. Therefore, it is possible to cool the amount of heat of about 400 Wby employing 10% of the entire laser gas stream for cooling the motor.Since the loss produced by the rotor 19 is actually about 12% of thetotal loss caused by the motor, the amount of the laser gas to flow inthe casing 18 may be 1/10 of 10% of the entire laser gas stream. The gaswhich has been used to cool the rotor is returned to an inlet 26 of theblower through a filter 23 for removing any grease from the laser gasand a flow control valve 24 for controlling the rate of flow of thelaser gas. Therefore, the optical parts of the laser oscillator deviceare prevented from being contaminated by the oil.

The other details than the turbo blower 15 are the same as those shownin FIG. 3. While the roots blower has an efficiency of about 35%, theturbo blower has an efficiency of about 80%. Therefore, the heatgenerated upon compression of the laser gas is lowered, and any coolingunit downstream of the blower may be dispensed with, or may be muchsmaller than if the roots blower were employed.

If the impeller of the turbo blower is made of a heat-resistant materialsuch as ceramic or the like, the cooling unit 8 may be dispensed with,and a cooling unit having the same capacity as that of the cooling unit8 may be located downstream of the blower (at the position of thecooling unit 7 shown in FIG. 3).

The present invention is particularly useful for a high-frequencyelectric-discharge CO₂ laser. If a DC electric discharge is used forlaser excitation, then a turbulent flow needs to be produced in thelaser gas for a uniform electric discharge. A roots blower is bestsuited to such an application since the blower requires a highcompression ratio. If a high-frequency electric discharge is requiredfor laser excitation, then it is not necessary to provide a turbulentflow in the laser gas, and hence a turbo blower having a low compressionratio and a high discharging capacity is effective as a blower.

With the present invention, as described above, since the gas blower isin the form of a turbo blower, the gas blower is small in size andweight, and the laser oscillator device is also small in size. The costof the laser oscillator device is lowered as the number of parts isreduced. The efficiency of the blower is increased, the running cost islowered, the amount of a laser gas to be replaced is reduced for areduction in the running cost, the laser gas undergoes no pulsation, andthe laser output power is not subject to fluctuations.

Since the motor for driving the turbo impeller is cooled, the turboimpeller can be rotated at high speed thereby to sufficiently cool thelaser gas, so that the oscillation efficiency of the laser oscillatordevice can be increased.

We claim:
 1. A laser oscillator device comprising an electric-dischargetube for producing an electric discharge in a laser gas contained in theelectric-discharge tube for laser excitation, an optical resonator foreffecting laser oscillation, and a gas circulating device having a gasblower and a cooling unit for forcibly cooling the laser gas,said gasblower comprising a turbo impeller that is rotatable in the laser gasand an electric motor for driving the turbo impeller, the electric motorhaving a stator that is cooled by thermal contact with a water- orair-cooled medium and a rotor that is cooled by contact with cooling gasflowing between the rotor and said stator, said gas circulating deviceincluding conduit means for directing the flow of said cooling gasbetween the rotor and the stator.
 2. A laser oscillator device accordingto claim 1, further including a pipe for passage of a gas for coolingsaid stator and said rotor, and a filter disposed in said pipe forremoving grease from said gas.